The present invention relates to a hydraulically operated striking mechanism including a striking piston, a control unit which alternatingly switches the movement of the striking piston and a tool receiving mechanism for receiving the insertion end of a drilling tool that is charged by the striking piston and is held so as to be displaceable in the longitudinal direction, independently of the striking piston.
When drilling rock and anchor holes, a drilling tool (drill bit) requires high striking rates, in conjunction with a low energy for the individual blows and a low contact pressure force, primarily during the start-up phase in view of normally unfavorable conditions for placement of the tool (for example, sloping and/or fissured surfaces). After the drilling tool has been centered, it is necessary, in order to realize optimum drill advance, to switch the striking mechanism to a low number of blows while simultaneously increasing the energy of the individual blows and increasing contact pressure. A corresponding control process would desirably take place if softer layers (for example, clay) or cavities are to be drilled through.
It is already known, for example from German Patent No. 2,658,455, to adapt a pressure medium operated striking mechanism to changing operating conditions by influencing the striking frequency by way of an externally supplied control pressure. In this connection it is possible to influence the control pressure as a function of the operating pressure of the contact pressure unit generating the contact pressure as a function of the operating pressure of a possibly existing rotation mechanism or by way of a manually adjusted pressure supply.